10 exam-style questions with answers and explanations, straight from our 1,030-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.
These 10 free PH questions are organized by exam domain, so you can see how each part of the Professional Hydrologist blueprint is tested. Reveal the answer and explanation under each question.
Domain 1: Water Quantity and Quality in the Field
Question 1
A project manager considers a low pesticide result reliable because the sample and its field duplicate agree closely. Field and laboratory blanks are clean. However, a laboratory matrix spike recovers 46% of the added pesticide, outside the project's 80-120% acceptance range; a laboratory control sample recovers 98%. What limitation has the manager overlooked?
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Correct answer: D - Matrix-related low bias remains possible despite the close agreement between duplicates.
Domain 2: Quantity and Timing of Flow
Question 2
An annual watershed balance reports 920 mm of precipitation, 280 mm of total streamflow at the outlet, and a 40 mm decline in total watershed water storage. Baseflow accounts for 170 mm of the reported streamflow. There are no water imports, exports, or net groundwater flows across the watershed boundary. All quantities are expressed as equivalent depths over the watershed. What annual actual evapotranspiration closes this balance?
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Correct answer: A - 680 mm
Question 3
For a steady-flow flood study, a mild-slope channel enters a reservoir whose pool creates backwater through the study reach. Flow remains subcritical. An analyst estimates each cross-section's water level independently from Manning's equation, using bed slope as friction slope. Which revision addresses the central hydraulic error?
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Correct answer: C - Use reservoir stage as the downstream boundary and calculate the backwater profile upstream.
Domain 3: Assessing Water Quality Conditions, Impacts and Sources
Question 4
A private-well sample has a confirmed nitrate concentration of 16 mg/L as nitrogen. The household uses the water to prepare formula for a two-month-old infant who has no reported symptoms. Bacterial testing is negative, and the owner asks what to do while the nitrate source is investigated. Which instruction addresses the immediate exposure risk?
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Correct answer: B - Use a verified safe alternative water source for preparing the infant's formula immediately.
Domain 5: Collection and Inventory of Basic Hydrological Data 31% of exam
Question 5
After a flood scours a streamgage's control riffle, three independent discharge measurements are consistently higher than the discharges predicted by the existing rating at the same gage heights. The electronic sensor agrees with the staff gage, and a leveling survey confirms that the datum has not moved. How should the hydrologist handle the record?
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Correct answer: C - Continue recording stage and develop a revised rating from the post-flood discharge measurements.
Domain 6: Interpretation, Analysis & Modeling of Hydrological Processes 46% of exam
Question 6
An ungated detention basin is routing a single-peaked inflow hydrograph. Its outlet is unobstructed, outflow increases with pool elevation, and rainfall on the pool, seepage, and evaporation are negligible. The inflow peak has passed, but the pool is still rising. What event marks the maximum pool elevation?
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Correct answer: B - The crossing at which inflow equals outflow and then becomes smaller than outflow.
Question 7
A stormwater outfall flows for two hours. During the first hour, discharge is 1.0 m³/s and suspended-sediment concentration is 40 mg/L. During the second hour, discharge is 5.0 m³/s and concentration is 20 mg/L. Each discharge and concentration is constant within its stated hour. What total suspended-sediment mass passes the outfall during the event?
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Correct answer: B - 504 kg
Domain 8: Collection and Inventory of Basic Hydrological Data 51% of exam
Question 8
A monitoring well yields low benzene concentrations although nearby depth-specific samples show substantial contamination in shallow sand. Its continuous screen crosses that sand, a clay separator, and a deeper, more permeable sand with much less benzene. The well will be properly decommissioned. What replacement design would measure each sand separately without creating an artificial pathway through the clay?
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Correct answer: D - Two short-screen wells with annular seals isolating each monitored sand interval.
Question 9
During low-flow sampling of a properly developed, short-screened monitoring well, the pump intake remains submerged within the screen. At 0.20 L/min, three successive readings meet the project's stabilization criteria for pH, specific conductance, dissolved oxygen, temperature, and turbidity. Drawdown is steady at 0.04 m, below the project's 0.10 m limit. Only 0.6 casing volume has been removed, but the procedure specifies no minimum purge volume. The sampler should now:
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Correct answer: A - Collect the sample while maintaining the established low pumping rate.
Domain 9: Interpretation, Analysis & Modeling of Hydrological Processes 38% of exam
Question 10
A conservative dissolved tracer enters a uniform sandy aquifer 180 m upgradient of a monitoring point along the groundwater flow path. Hydraulic conductivity is 12 m/day, hydraulic gradient is 0.020, effective porosity is 0.20, and total porosity is 0.40. Assume steady one-dimensional flow and neglect dispersion, sorption, and reaction. What is the predicted advective travel time to the monitoring point?